As one of this kind of substrate processing apparatuses, there is known a parallel place type plasma processing apparatus in which a lower electrode and an upper electrode are arranged in parallel to each other in a processing chamber. In this apparatus, the lower electrode also serves as a mounting table for mounting thereon a processing target substrate (hereinafter, simply referred to as a “substrate”) such as a semiconductor wafer, and the upper electrode serves as a shower head for discharging a gas toward the substrate. This plasma processing apparatus is configured to generate plasma by applying a high frequency power between the upper and lower electrodes after supplying a gas onto the substrate from the shower head, and is configured to perform a certain process such as a film forming process or an etching process by the plasma.
As for such a plasma processing apparatus, in order to improve uniformity of the substrate process in a surface of the substrate, it has been proposed to partition an inside of the shower head into plural gas rooms and connect gas supply lines to the gas rooms, respectively (see, for example, Patent Documents 1 and 2). By way of example, with this configuration, by discharging a gas onto the substrate from gas holes in a vicinity of a center portion of the substrate (center gas holes) and gas holes in a vicinity of an edge portion of the substrate (edge gas holes), gas concentrations in the surface of the substrate can be locally adjusted. Accordingly, the uniformity of the substrate process such as etching process in she surface of the substrate can be improved.
Patent Document 1: Japanese Patent Laid-open Publication No. H08-158072
Patent Document 2: Japanese Patent Laid-open Publication No. H09-045624
Patent Document 3: Japanese Patent Laid-open Publication No. H10-064888
The gases discharged from the respective gas holes of the shower head are gradually diffused downward. Accordingly, like Patent Documents 1 and 2, if the gas is discharged from the center gas holes and the edge gas holes, the gas discharged from the edge gas holes may be diffused to the central portion of the substrate depending on the positions of the edge gas holes. In such a case, the process on the edge portion of the substrate may not be controlled accurately.
By way of example, in Patent Documents 1 and 2, this problem is not particularly mentioned, and the center gas holes and the edge gas holes are uniformly arranged, and discharging openings of the center and edge gas holes are formed on the same flat plane. Accordingly, as the distance between the discharging openings of the edge gas holes and the substrate increases, the diffusing range of the gas discharged from the edge gas holes also becomes increased, and the influence on the process on the central portion of the substrate is also increased. As a result, controllability of the process on the edge portion of the substrate is deteriorated.
Further, in Patent Document 3, it is described that a thickness of a central portion of a gas diffusion plate having gas holes is set to be smaller than a thickness of an edge portion of the gas diffusion plate in order to improve heating efficiency of the gas diffusion plate. With this configuration, since the positions of gas holes on the edge portion thereof are located at positions lower than those of the gas holes provided on the central portion thereof, diffusion of a gas discharged from the gas holes provided on the edge portion may be suppressed.
Patent Document 3, however, does not describe the diffusion of the gas discharged from the gas holes provided on the edge portion. Furthermore, Patent Document 3 is mainly focused on improving the heating efficiency of the gas diffusion plate.
Accordingly, in order to obtain uniform mass of the gas diffusion plate over the central portion and the edge portion of the gas diffusion plate even when the thickness of the central portion of the gas diffusion plate is set to be small, the gas holes on the edge portion are set to be larger than the gas holes on the center portion. As a consequence, the diffusing range of the gas discharged from the gas holes on the edge portion is more increased. Accordingly, the influence on the process on the central portion of the substrate is increased.